3GPP LTE (3rd Generation Partnership Project Long Term Evolution: hereinafter abbreviated as “LTE”) adopts single-carrier transmission whereby data signals are allocated to a continuous band on an uplink. FIG. 1A shows how frequency resources are allocated in single-carrier transmission. Single-carrier transmission has a characteristic that its CM (Cubic Metric) is small. Therefore, single-carrier transmission makes it possible to reduce the backoff of a power amplifier for transmitting a transmission signal without distortion, increase maximum transmittable power, and thereby expand the cell coverage.
Furthermore, 3GPP LTE-Advanced (3rd Generation Partnership Project Long Term Evolution-Advanced: hereinafter abbreviated as “LTE-Advanced”) which is an improvement on LTE is studying the adoption of multicluster transmission on an uplink. FIG. 1B illustrates how frequency resources are allocated in multicluster transmission. As shown in FIG. 1B, data signals are allocated to a plurality of discontinuous clusters in multicluster transmission. Here, the “cluster” refers to a plurality of carrier groups in frequency resource allocation. FIG. 1B shows an example of multicluster transmission where the number of clusters is 2.
As shown in FIG. 1B, since data signals are allocated to discontinuous carrier groups in multicluster transmission, multicluster transmission can improve a frequency diversity gain compared to single-carrier transmission. On the other hand, CM increases in multicluster transmission compared to single-carrier transmission.
In LTE-Advanced, studies are underway about a transmission method to switch between single-carrier transmission and multicarrier transmission on an uplink.
In LTE and LTE-Advanced, there are cases where data signals and control it formation signals are simultaneously transmitted on an uplink. In this case, the data signals and the control information signals need to be multiplexed and transmitted. There are two methods of multiplexing data signals and the control information signals; time multiplexing (TDM: Time Division Multiplexing) and frequency multiplexing (FDM: Frequency Division Multiplexing).
Hereinafter, a case will be described where time division multiplexing and frequency division multiplexing are used as the methods of multiplexing data signals and control information signals on an LTE uplink. Examples of a control information signal to be multiplexed with a data signal include a response signal such as ACK/NACK for the data signal transmitted on a downlink, but the control information signal is not limited to this.
[1] Time Division Multiplexing (See FIG. 2)
In time division multiplexing, a control information signal is transmitted using the same frequency resource as that of a data signal. Applying time division multiplexing to an LTE uplink results in single-carrier transmission, and therefore can maintain low CM. However, on the LTE uplink, a frequency resource for allocating a control information signal (hereinafter referred to as “control information resource”) is provided on a frequency different from a frequency resource for allocating a data signal (hereinafter referred to as “data resource”). To be more specific, on the LTE uplink, control information resources are provided on PUCCHs (Physical Uplink Control CHannel) located at both ends of a system band. Therefore, when a control information signals are allocated to data resources through time division multiplexing, the efficiency of use of data resources deteriorates.
[2] Frequency Division Multiplexing (See FIG. 3)
In frequency division multiplexing, a control information signal is transmitted allocated to a control information resource which is different from a data resource. Therefore, frequency division multiplexing can avoid the efficiency of use of data resources from deteriorating. However, when frequency division multiplexing is applied to an LTE uplink, data signals and control information signals are transmitted using multicluster transmission, which causes CM to increase compared to single-carrier transmission.
Thus, time division multiplexing which enables low CM single-carrier transmission is adopted for an LTE uplink (see non-patent literature 1)